The easiest is to install manual hubs; only the hubs need to be installed and this is a bolt off bolt on operation. Of course you would need to go out of vehicle to turn them on an off.
Keeping the hubs always ON consumes fuel...and drag from the front gear train can be a hazard when cold and slippery road are combined with 2WD; the rear will try to push against the dragging front end with hairy results.
I have the WARN auto-mechanical . THis is a complete kit that requires more installation work as described here
http://www.geocities.com/lmp4203/kia...hubinstall.pdf and you will have to cut the tip off hub caps covers to make room
http://www.geocities.com/lmp4203/kiasport/dscn1696.jpg as for the manuals.
THe main difference compared to the original vacuum models is they must be engaged from a standstill only; T-case can be turned back to 2WD on the fly, but the hubs will not disengage until you stop and back-off 5 feet, otherwise you are in same condition as described above: front end dragging the rear.